The present invention relates to a battery pack used in, a lithium ion polymer secondary battery, for example, and a method of manufacturing such battery pack.
In recent years, portable electronic apparatuses, such as laptop personal computers, portable phones, and PDAs (personal digital assistant), have been widely introduced to the market, and, as a power source for such apparatuses, a lithium ion battery has been widely used having advantages, such as provision of high voltage, high energy density, and being lightweight.
Further, lithium ion polymer secondary batteries have been put into practical use in order to solve the problem of leakage of liquid, which may occur when using an electrolyte in a liquid state. Examples of such batteries are lithium ion polymer secondary batteries using, as an electrolyte, a gelatinized polymer film comprising a polymer impregnated with a non-aqueous electrolytic solution, or an electrolyte in a solid state.
The polymer lithium ion battery has a construction of a cell including a battery element which has a positive electrode, a negative electrode, and a polymer electrolyte, wherein the positive electrode and the negative electrode are respectively electrically connected to leads, and which is covered with a packaging film, e.g., an aluminum laminate. Further, the cell and a wiring board having a circuit portion mounted thereon are together housed in a box-form plastic molded case comprising upper and lower cases.
For example, Japanese Laid-Open Patent Application No. 2002-260608 has a description of an example of the lithium ion polymer secondary battery having the above construction.
Conventionally, leads, which are connected to the positive electrode and the negative electrode of a battery element, have been bonded to a circuit board by resistance welding and housed in a plastic molded case, together with the battery element.
In the present specification, a strip-like positive electrode, a strip-like negative electrode, and a polymer electrolyte and/or a separator disposed between the positive and negative electrodes, which are stacked on one another and spirally wound together in a longitudinal direction, wherein the positive electrode and the negative electrode are respectively electrically connected to lead terminals, is referred to as “battery element”. A battery element that is covered with an outer covering (package) is referred to as “cell”. The cell that further has a circuit board having mounted thereon a circuit, such as a protective circuit, is referred to as “battery pack”.
The conventional construction of the battery using a box-form molded case has a drawback in that the thickness is increased. The conventional cell has been improved in order to solve the existing problems and studies have been made on a cell covered with neither upper nor lower molded cases in a thicknesswise direction of the cell, or a cell using a thin metal plate as package. In these cells, a resin mold is inserted into the cover from both the edge faces of the cell. With respect to the conventional battery pack, the constituent parts of the battery pack are assembled after the cell is finished. In addition, the assembly lines for the cell and the battery pack are separated from each other.
FIG. 15 shows a view for explaining how a circuit board is fitted in the conventional battery pack. In the battery pack having a conventional construction, the circuit board has been housed in a container space defined by a packaging film while bending leads connected respectively to the positive electrode and the negative electrode of the battery element.
In FIG. 15, reference numeral 21 designates a circuit board. The circuit board 21 has mounted thereon a protective circuit having a protective element, such as a PTC, a fuse, or a thermistor, or the like. In addition, a lead 22 of the battery element is bonded to the circuit board 21 by resistance welding. The circuit board 21 is turned 90° in a clockwise direction and disposed in an opening in the edge face on the top side of an package 23 for containing the cell, and then placed in an exclusive die and subjected to resin mold integral molding.
However, in the conventional battery pack having the above construction, leads are bent by means of a jig or by hand and incorporated into the packaging film, and therefore a problem arises in that the bent form of the leads is not made stable. In addition, a die for integral molding and an exclusive injection molding machine for integral molding are needed, and further a problem occurs in that the temperature elevation caused during the resin molding adversely affects the IC parts or soldering portions on the circuit board.
With respect to the conventional battery pack, the constituent parts of the battery pack are assembled after the cell is finished. In addition, the assembly lines for the cell and the battery pack are separated from each other. Therefore, there has been a problem in that the production process for the battery pack is complicated. On the other hand, a method in which the cell is finished and then the cell and a resin mold portion are subjected to integral molding is known, but this method has problems in that the temperature elevation caused during the resin molding adversely affects the IC parts or soldering portions on the circuit board, and that the dimensional accuracy of the battery pack is poor.